A Class-E amplifier converts a DC source to an amplified output signal that is sinusoidal, at a certain frequency. Class-E amplifiers are typically highly efficient switching power amplifiers.
FIG. 1 shows a conventional Class-E amplifier device 100. The device 100 includes an input power VP. A first terminal of an input inductor 110 is coupled to the input power VP. A drain of a MOSFET 112 is coupled with a second terminal of the input inductor 110 and an input terminal of a resonant LCR load or resonant load 111 having a resonant frequency. A driving module 122 is coupled with a gate of the MOSFET 112 for driving the MOSFET 112. The driving module 122 alternatively turns the MOSFET 112 on and off at a fixed frequency in response to an input signal ‘Vin(freq)’. The fixed frequency is equal to the resonant frequency of the resonant load 111.
The input inductor 110 is typically a large inductor connected to the input power VP. The power stored in the input inductor 110 can be pulled down to a circuit ground through the power MOSFET 112 when the MOSFET 112 is turned on. When the MOSFET 112 is not conducting, the power in the inductor 110 is coupled to the resonant load 111. The resonant load 111 includes a first capacitor 114 coupled from the input terminal to the circuit ground. A second capacitor 116 is coupled is series with an inductor 118 between the input terminal of the resonant load 111 and an output terminal of the resonant load 111. A load circuit 120 is coupled between the output terminal of the resonant load 111 and the circuit ground. The Class-E device 100 operates the MOSFET 112 to be either in the Ohmic region or completely off.
When the MOSFET 112 is not conducting, the voltage on the drain Vdrain(freq) will go high and can be higher than the DC input voltage VP. When the MOSFET 112 turns on, the voltage on the drain Vdrain(freq) goes to the Ohmic voltage drop of the MOSFET 112. The low impedance of the MOSFET 112 causes the power that is consumed by the MOSFET 112 to be low.
In order for the device 100 of FIG. 1 to provide a single output sinusoidal voltage amplitude at a single frequency, there has to be a fixed relation between the input frequency to the MOSFET 112, the duty cycle of the input signal at this input frequency and the values of the components making up the resonant LCR load 111. Deviating from this fixed relation results in an increase of undesired harmonic distortion or reduced efficiency or both. Hence, devices similar to the device 100, attempting to effect the amplitude of the output VOUT by regulating the duty cycle of the input frequency, or by varying the LCR values will be subject to this increased harmonic distortion and reduced efficiency.
FIG. 2 shows another conventional Class-E amplifier device 200. The device 200 is similar to the device 100 of FIG. 1 except a buck converter circuit 225 is coupled between an input power source VP and an input inductor 210. In particular, the input inductor 210, the MOSFET 212, the capacitors, 214 and 216, the inductor 218, the load circuit 220 and the driving module 222 correspond in function and architecture to the input inductor 110, the MOSFET 112, the capacitors 114 and 116, the inductor 118, the load circuit 120 and the driving module 122, respectively, of FIG. 1. The buck converter circuit 225 includes a switch 224 having a first terminal coupled to the input power VP and a second terminal. A diode 226 has a cathode and an anode. The cathode is coupled to the second terminal of the switch 224 and the anode is coupled to the circuit ground. A buck inductor 228 has a first terminal coupled to the cathode and a second terminal coupled to the first terminal of the input inductor 210. A buck capacitor 230 has a first terminal coupled to the second terminal of the buck inductor 228 and a second terminal coupled to ground. Like the embodiment of FIG. 1, the driving frequency of a MOSFET 212 is fixed at the resonant frequency of the resonant load 211. The device 200 uses the buck converter 225 to adjust the amplitude of the output voltage VOUT. The buck converter 225 adjusts the amplitude of the output voltage VOUT by varying or modulating the amplitude of the input power VP. The buck converter 225 operates in the usual manner of conventional buck converters. The use of the buck converter circuit 225 allows the amplitude of the E-Class amplifier circuit 200 to be adjusted. Undesirably, the buck converter 225 will reduce the overall efficiency of the E-Class amplifier circuit 200. Additionally, the buck converter 225 requires additional discrete components which will increase the cost and complexity of the circuit 200.
FIG. 3 shows another conventional Class-E amplifier device 300. The device 300 is a differential amplifier. An input power VP is coupled to a first terminal of a matching first and second input inductor 310A, 310B. A drain terminal of a first and second MOSFET 312A, 312B is coupled with a second terminal of the first and second input inductors 310A, 310B, respectively. A resonant LCR load or resonant load 311 is coupled between the second terminals of the first and second input inductors 310A, 310B. A driving module 322 is coupled with a gate of the first and second MOSFET 312A, 312B for driving the first and second MOSFET 312A, 312B. The driving module 322 alternatively turns the first and second MOSFET 312A, 312B on and off at a fixed frequency in response to an input signal Vin(freq) (not shown). The fixed frequency is equal to a resonant frequency of the resonant load 311.
The first and second input inductor 310A, 310B are typically large inductors connected to the input power VP. The power stored in the first and second input inductor 310A, 310B can be pulled down to the circuit ground through the first and second MOSFET 312A, 312B when the first and second MOSFET 312A, 312B are turned on. When the first and second MOSFET 312A, 312B are not conducting, the power in the first and second input inductor 310A, 310B are coupled to the resonant load 311. The resonant load 311 includes a matching first and second capacitors 314, 315, respectively. The first and second capacitors 314, 315 are coupled from the second terminals of the first and second input inductor 310A, 310B, respectively, to the circuit ground. A third or series capacitor 316 is coupled in series with a load circuit 320 and an inductor 318. An output terminal ‘Vout’ is coupled to a first and a second terminal of the load circuit 320. The Class-E device 300 operates the first and second MOSFET 312A, 312B to be either in the Ohmic region or completely off.
When the first and second MOSFET 312A, 312B are not conducting, the voltage on the drain Vdrain(freq) will go high and can be higher than the DC input voltage VP. When the first and second MOSFET 312A, 312B turn on, the voltage on the drain Vdrain(freq) goes to the Ohmic voltage drop of the first and second MOSFET 312A, 312B. The low impedance of the first and second MOSFET 312A, 312B cause the power that is consumed by the first and second MOSFET 312A, 312B to be low.
In order for the device 300 of FIG. 3 to provide a single output sinusoidal voltage amplitude at a single frequency, there has to be a fixed relation between the input frequency to the first and second MOSFET 312A, 312B, the duty cycle of the input signal at this input frequency and the values of the components making up the resonant LCR load 311. Deviating from this fixed relation results in an increase of undesired harmonic distortion or reduced efficiency or both. Hence, devices similar to device 300, attempting to effect the amplitude of the output VOUT by regulating the duty cycle of the input frequency, or by varying the LCR values will be subject to this increased harmonic distortion and reduced efficiency.
FIG. 4 shows another conventional Class-E amplifier device 400. The device 400 is similar to the device 300 of FIG. 3 except a buck converter circuit 425 is coupled between an input power source VP and a first and second input inductor 410A, 410B. In particular, the first and second input inductor 410A, 410B, a first and second MOSFET 412A, 412B, a first and second capacitor, 414 and 415, a series capacitor 416, an inductor 418, a load circuit 420 and a driving module 422 correspond in function and architecture to the first and second input inductor 310A, 310B, the first and second MOSFET 312A, 312B, the first and second capacitor, 314 and 315, the series capacitor 316, the inductor 318, the load circuit 320 and the driving module 322, respectively, of FIG. 3. The buck converter circuit 425 includes a switch, diode, inductor and capacitor (FIG. 2). Like the embodiment of FIG. 3, the driving frequency of the first and second MOSFET 412A, 412B is fixed at the resonant frequency of the resonant load 411. The device 400 uses the buck converter 425 to adjust the amplitude of the output voltage VOUT. The buck converter 425 adjusts the amplitude of the output voltage VOUT by varying or modulating the amplitude of the input power VP. The buck converter 425 operates in the usual manner of conventional buck converters. The use of the buck converter circuit 425 allows the amplitude of the E-Class amplifier circuit 400 to be adjusted. Undesirably, the buck converter 425 will reduce the overall efficiency of the E-Class amplifier circuit 200. Additionally, the buck converter 225 requires additional discrete components which will increase the cost and complexity of the circuit 400.
Accordingly, it is desirable to provide a Class-E amplifier device which is more efficient and more economical to produce. In addition it is desirable to provide a Class-E amplifier device that provides optimization of power transferred to a load circuit.